1. Field of the Invention
The present invention relates to a lubricating device in an automatic transmission which is capable of supplying lubricating oil accurately in accordance with the engagement state of a plurality of clutches within the automatic transmission.
2. Description of the Related Art
One type of conventional automatic transmission has a speed change mechanism for shifting the rotation of an input shaft between a plurality of speeds by selectively connecting a speed reducing planetary gear set for reducing the rotational speed of the input shaft and for transferring rotation at the reduced speed to each element of a planetary gear set including a plurality of planetary gear subsets, via a plurality of clutches and brakes. A first clutch is disposed within a first drum having a closed-end cylindrical shape, and a second clutch is disposed within a second drum which has a closed-end cylindrical shape and which is mounted inside the first drum.
When the first and second clutches are engaged, the amount of heat generated increases. Therefore, lubricating oil is typically supplied by centrifugal force in a radial direction from a lubricant supply passage provided in the input shaft for lubrication of the friction engagement elements of the clutches and brakes, the meshing portions of the planetary gears, and various bearings.
In the above-described type of automatic transmission, the amount of heat generated varies greatly depending on whether the clutch is engaged or disengaged, but conventionally, a constant amount of lubricating oil is supplied at all times, irrespective of the state of engagement. Hence in certain cases, although the overall flow rate of the lubricating oil that is supplied through the supply passage is sufficient, the amount of lubricating oil supplied to specific locations where a large amount of heat is generated may be deficient.
To address the above-described problem, the overall flow rate of the lubricating oil may be increased responsive to an increase in the amount of heat generated as a reference, but since the amount of heat generated by a frictional engagement element varies according to its state of engagement and its rotational speed, the result may be supply of an appropriate amount of to the specific locations where a large amount of heat is currently generated, but supply of an excessive amount of oil to other locations.